Percussive drilling tool with exhaust chamber



J. M. CLEARY 3,187,823

PERCUSSIVE DRILLING TOOL WITH EXHAUST CHAMBER June 8, 1965 Filed Feb. 11, 1965 Fig. 2

INVENTOR.

James M. Cleury BY I'll/A Q4 w w m Attorney United States Patent 0 Purl! 3,187,823 PER JUSSIVE DRELHNG TOUT. WlTi-l EXHAUST HAMEER James M. Cleary, Dalias, Ten, assignor to The Atlantic Refining Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Feb. 11, 1963, Ser. N 257,466 8 Claims. (Ci. 2173-69) This invention relates to percussive earth borehole drilling with gaseous power fluids wherein operation of the percussive unit is less sensitive to fluid pressure changes exterior of the percussive unit.

In percussive drilling, a hammer reciprocates within a power unit to impact an anvil which in turn forces a drill bit against an earth formation. In fluid operated percussive units, flow of the power fluid through the power unit controls the movement of the hammer. In some units, the power fluid moves the hamrner in only one direction of its reciprocal movement; while in others, and more preferred units, the power fluid moves the hammer in first one direction and then in the other direction. In moving the hammer in one direction, power fluid at a relatively high pressure flows into a power chamber forming part of the power unit. The pressure of this fluid causes the hammer to move and the volume of the power chamber occupied by high pressure power fluid increases until the hammer reverses direction. Thereupon, the high pressure power fluid in this power chamber is quickly discharged to an exhaust chamber where the fluid flows to and through openings in the drill bit. If the hammer is .reciprocated by power fluid in both directions, two discrete volumes of high pressure power fluid are discharged into the exhaust chamber during one cycle of the hammer.

In prior gaseous-fluid operated percussive units, the pressure drop across the openings in the bit is small since the cross-sectional area of flow of these openings is at least equal to the cross-sectional area of flow of the exhaust chamber. In such prior devices, the volume of the power chamber is also relatively small so the fluid pressure in the exhaust chamber fluctuates over a wide range between the ambient borehole pressure and the pressure of the power fluid discharged from the power chamber.

The efliciency of gaseous-fluid operated percussive units depends in part on the compressibility and pressure of the power fluid in different parts of the percussive unit. Maximum efficiency is obtained by adjusting the size, shape and strength of the parts of the percussive unit. In prior devices, the operating pressures inside of the per cussive unit are continually changing since the fluid pressure in the exhaust chamber fluctuates over a wide range and the back pressure in the exhaust chamber exerted by the fluids in the borehole increases as the hole deepens. This adversely affects the efliciency of the percussive unit and, frequently, it is necessary to remove the percussive unit and change or modify parts of the percussive unit. This is costly and time consuming.

It is, therefore, a desirable object of this invention to provide a percussive drilling system that is less sensitive to borehole pressure changes for much greater borehole distances than heretobefore experienced. Such a unit will operate more uniformly than prior percussive drilling units over greater borehole distances and reduce the frequency and need for costly and time consuming modifications.

Another object of this invention is to provide a compressible fluid-operated percussive unit in which the etheiency of the percussive unit is rendered practically independent of the pressure differential existing between the power fluid interiorly and exteriorly of the percussive unit.

A further object is to provide a gaseous-fluid operated 'ice percussive drilling unit that maintains a pressure drop across the openings in the bit whereby the openings are less susceptible to plugging.

Still a further object is to provide a gaseous-fluid operated percussive unit wherein the high pressure power fluid is discharged to a nearby constant pressure exhaust chamher.

For a complete understanding of the present invention and for further objects and advantages thereof, reference should be had to the following description, appended claims and accompanying drawings in which:

FIGURE 1 is a longitudinal view, partly in section, of a percussive drilling unit constructed in accordance with this invention;

FIGURE 2 is a simple schematic of the most important features of the gaseous-fluid operated percussive drilling unit of this invention.

In this invention, high pressure power fluid in a power chamber of the percussive unit is discharged to an exhaust chamber having a volume substantially largerthan the volume of the power chamber. The large volume of the exhaust chamber greatly reduces pressure fluctuations in the exhaust chamber. The outlet of the exhaust chamber is a nozzle sized to make the average fluid velocity through the minimum cross-sectional area of flow of the exhaust chamber sub-sonic and the average flow velocity through the nozzle sonic when the pressure exterior of the percussive unit is low. The cross-sectional area of flow of the nozzle or nozzles is substantially smaller than the minimum cross-sectional area of flow of the exhaust chamber. Moreover, the foregoing features of the percussive unit are adapted to maintain the fluid pressure in the exhaust chamber at a level substantially higher than the ambient bottom hole pressure exterior of the percussive unit for a predetermined depth of the borehole.

For compressible fluids, if the pressure upstream of a nozzle is substantially greater than the pressure downstream of the nozzle, changes in the downstream pressure have much less effect on the upstream pressure than when the upstream and downstream pressures are nearly equal. If the pressure upstream of the nozzle is at least twice as great as the downstream pressure, fluid flow through the nozzle will be sonic and the upstream pressure will be substantially independent of the downstream pressure. These principles will aid in understanding the following description of this invention.

Consider now how gaseous-fluid operated earth drilling percussive units may be improved by the present invention by referring first to FIGURE 1 wherein is shown an improved percussive drilling unit of the type described in detail in copending application Serial No. 167,121, filed January 18, 1962, by the same inventor and owned by a common assignee as the present invention.

The percussive unit includes casing 11 fluidly communicating with drill string 13 which conducts power fluid from a suitable source at the surface of the earth to the downhole percussive unit. The pressure of the power fluid in drill string 13 is controlled by the operator to accomplish the objectives of this invention.

In the lower end of casing 11 is bit-anvil unit 15 which is impacted by reciprocating hammer 17. Upward movement of the hammer away from the bit-anvil unit is herein termed the return stroke and downward movement toward the bit-anvil unit is called the power stroke.

Hammer 17 is slideably mounted about exhaust tube 19 which extends downwardly into the top portion of bitanvil unit 15. The upper end of exhaust tube 19 is sealed into the inlet end of casing 11 and has power stroke inlet ports 21 which are above hammer 17. Extending into the upper end of exhaust tube 19 is blowing power fluid tube 23 whose lower end seals against the inner wall of the stabilize operation of the percussive unit as hereafter pointed out.

Below power stroke inlet ports 21 in exhaust tube 19 is exhaust chamber inlet port 29 which is opened and closed by movement of hammer 17 to alternately communicate with upper power chamber 31 above the hammer and lower power chamber 33 below the hammer. Since this invention is concerned with the amount of high pressure power fluid dumped into the exhaust chamber from these power chambers, the size and volume of these power chambers is important. It should also be noted that shape of these power chambers will depend on the type of percussive unit. As used herein, the word chamber includes all passages, cavities and openings interconnected when the power chamber opens to discharge high pressure power fluid into exhaust tube 19 by way of exhaust chamber inlet port 29. As the hammer reciprocates, the volume and size of these chambers continually changes; but, for reasons best understood by reference to the rest of this description, it is the volume and size of the power chamber at the moment that it is opened to the exhaust chamber that is important.

In the wall of casing 11 is return stroke inlet passage 35 which connects lower power chamber 33 with the power fluid inlet section of casing 11.

Return stroke inlet passage 35 and power. stroke inlet passage 21 are alternately opened and closed to incoming high pressure power fluid by suitable valve means (not shown) in the power fluid inlet section of casing 11 to cause hammer 17 to reciprocate within casing 11.

Returning to the exhaust tube and bit-anvil unit, there is shown exhaust chamber 37 which includes all of the volume in exhaust tube 19 and bit-anvil unit which would normally undergo a pressure change as high pressure power fluid from either upper power chamber 31 or lower power chamber 33 is discharged through exhaust chamber inlet port 29. The size and volume of exhaust chamber 37 is also important as. hereafter pointed out, and is related to the size .and volume of the larger of upper power chamber 31 and lower power chamber 33. Like the power chambers, the hape of exhaust chamber 37 will depend on the type of percussive unit. This chamber includes all interconnecting passages, openings and cavities. receiving high pressure power fluid from the power chamber. At some point, exhaust chamber 37 will have a minimum cross-sectional area of flow through which the power fluid flows. In FIGURE 1, this is the inside cross-sectional area of exhaust tube 19..

In the lower working end surface of bit-anvil 15 is nozzle means 39 through which the power fluid is discharged to borehole 41. Nozzle means 39 could be placed above "the bits working surface provided that all of the power fluid discharged into the exhaust chamber passes through the nozzle means; but preferably, for many reasons, the nozzle means should be at the bits working surface. For example, the pressure drop across the nozzle mean will prevent plugging of the bit. Nozzle means 39 is any type of flow channel in which the fluid velocity is increased and the pressure is decreased, e.g., an orifice, a convergent short tube and the like. The total minimum cross-sectional area of flow through the nozzle means is important as hereafter shown and is related to the minimum cross-sectional area of flow of the exhaust chamber and operating conditions of the percussive unit.

The relationships between the size of the power chambers, size of the exhaust chamber, and minimum crosssectional areas of flow of the exhaust chamber and nozzle means will be best understood by reference to FIGURE 2 along with FIGURE 1. FIGURE 2 schematically shows the maximum volume of power fluid dumped into the exhaust chamber at any one time, which, in FIGURE 1, would be the volume of the larger of upper. power chamber 31 and lower power chamber 33 at the moment that these chamber open to dump high pressure power fluid into the exhaust chamber. At this point, it should be recalled that in some power units, the power fluid moves the hammer in only one direction and such units have only one power chamber which is opened to the exhaust chamber. In other power units like the one described herein, the power fluid moves the hammer in both directions and there are two power chambers which are alternately opened to the exhaust chamber. The invention applies to either type of gaseous-fluid operated percussive unit.

As indicated in FIGURE 2, this maximum volume of power fluid is discharged through exhaust chamber inlet port 29 to exhaust chamber37 having a volume substantially larger than the volume of the larger power chamber. The power fluid flows through the minimum cross-sectional area of flow of exhaust chamber 37 which is the inside cross-sectional area of exhaust tube 19. The gas flows out of the exhaust chamber by way of nozzle means 39 which has a total minimum cross-sectional area of flow substantially less than the minimum cross-sectional area of flow of the exhaust tube. The schematic shows only one nozzle since it is the total area of flow of the nozzle or nozzles that is controlling and not the number of nozzles.

In this invention, the volume of exhaust chamber 37 must be at least 1.5 times the maximum power chamber volume and, preferably, will be at least twice as large as the power chamber volume. Preferably, the volume of the exhaust chamber will be such that pressure fluctuationsinside of the exhaust chamber will be less than plus or minus twenty percent when the pressure inside of the exhaust chamber is at least 1.2 times the pressure exterior of the percussive unit. The volume needed depends on the type, size and operating conditions of the percussive unit and the areas of flow herein mentioned. Preferably,

V such pressure fluctuations will be less than ten percent when the pressure inside the exhaust chamber is at least two times as great as the ambient pressure.

The total minimum cross-sectional area of flow of nozzle means 39 is related to the minimum cross-sectional area of flow in exhaust chamber 37 to carrying out the above conditions. The total minimum cross-sectional area of flow of the nozzle means should be substantially less than the minimum cross-sectional area of flow through the exhaust chamber. Preferably, the minimum crosssectional area of flow in the exhaust chamber through which the power fluid flows should be at least 1.5 times as great as the total flow area of the nozzle means, and, even more preferably, will be at least 1.9 times as great. The actual ratio required also depends on the type, size and operating conditions of the percussive tool. The minimum cross-sectional area of flow of the exhaust chamber should be large enough to render the average fiow rate theret'hrough substantially less than 1120 feet per second (sub-sonic) while the. total minimum crosssectional area of flow of the nozzles should be small enough to make the flow rate sonic when the pressure exterior of the percussive unit is atmospheric. Preferably, flow through the nozzles will be sonic during drilling of the first 1,000 feet of borehole when the ambient bottom hole pressure is relatively low.

From the above description, it should now be apparent that central bore passage 27 of blowing power fluid tube 23 may be sized to fit the design and operating conditions of the percussive unit to continually bleed enough high pressure gas into the exhaust chamber to aid in maintaining the desired stable pressure level.

The improved process for earth borehole percussive drilling involves circulating a gaseous power fluid through a percussive drilling unit to reciprocate a hammer which periodically impacts a drill bit against an earth formation. The operator controls the pressure of the incoming power fluid to a level which maintains the pressure of the exhaust chamber at a pressure at least 1.2 times as great as the fluid pressure exterior of the percussive unit. Preferably, during drilling of the first one thousand feet of borehole, the operator maintains the incoming power fluid pressure at a level where the exhaust chamber pressure is at least two times as great as the fluid pressure exterior of the percussive unit.

It will be evident that this invention is applicable to various types of gaseous operated percussive earth drilling units and that changes in the details disclosed herein may be adopted without departing from the spirit of this invention as set forth.

I claim:

1. In gaseous-fluid operated percussive earth borehole drilling units wherein a drilling means is periodically impacted against an earth formation by a hammer which is reciprocated within said percussive unit and at time spaced intervals a power chamber containing said gaseous fluid at relatively high pressure opens to an exhaust chamber, the improvement comprising an exhaust chamber having an inlet adapted to receive gaseous fluid from said power chamber and an outlet consisting of nozzle means, said exhaust chamber having a volume at least 1.5 times as great as the volume of said power chamber and having a minimum cross-sectional area of flow between said inlet and said outlet at least 1.5 times as great as the minimum cross-sectional area of flow of said nozzle means.

2. The improvement of claim 1 wherein the volume of the exhaust chamber is at least two times as great as the volume of the power chamber.

3. The improvement of claim 1 wherein the minimum cross-sectional area of flow of the exhaust chamber between the inlet and outlet is at least 1.9 times as great as the minimum cross-sectional area of flow through the nozzle means.

4. The improvement of claim 1 wherein the nozzle means forming the outlet of the exhaust chamber is in the working surface of the drilling means.

5. The improvement of claim 1 wherein the volume of the exhaust chamber and the minimum cross-sectional area of flow of the nozzle means are adapted to maintain a relatively constant pressure within said exhaust chamber varying less than twenty percent during reciprocation of the hammer.

6. The improvement of claim 1 wherein the volume of the exhaust chamber, minimum cross-sectional area of flow of the exhaust chamber between inlet and outlet and the minimum cross-sectional area of flow of the nozzle means are adapted to maintain the average pressure in the exhaust chamber at a value at least double the pressure ambient of the percussive unit when the percussive 7 unit is at the earths surface while maintaining enough pressure drop in said percussive unit to operate said percussive unit.

7. The improvement of claim 1 wherein the volume of the exhaust chamber and the minimum cross-sectional area of flow of the nozzle means are adapted to maintain the pressure within the exhaust chamber at a value at least 1.2 times as great as the pressure ambient of the percussive unit during reciprocation of the hammer means.

8. The improvement of claim 1 wherein the volume of the exhaust chamber, minimum cross-sectional area of flow of the exhaust chamber between the outlet and inlet and the minimum cross-sectional area of flow of the nozzle means are adapted to maintain the average pressure in the exhaust chamber at a value at least double the fluid pressure in the borehole surrounding the percussive unit during drilling of the first 1,000 feet of borehole, while maintaining enough pressure drop in said percussive unit to operate said percussive unit.

References Cited by the Examiner UNITED STATES PATENTS 1,861,042 5/32 Zublin 17373 1,902,562 3/33 Lear 17373 2,979,033 4/61 Bassinger 17373 3,111,176 11/63 Wilder 175-92 BENJAMIN HERSH, Primary Examiner. 

1. IN GASEOUS-FLUID OPERATED PERCUSSIVE EARTH BOREHOLE DRILLING UNITS WHEREIN A DRILLING MEANS IS PERIODICALLY IMPACTED AGAINST AN EARTH FORMATION BY A HAMMER WHICH IS RECIPROCATED WITHIN SAID PERCUSSIVE UNIT AND AT TIME SPACED INTERVALS A POWER CHAMBER CONTAINING SAID GASEOUS FLUID AT RELATIVELY HIGH PRESSURE OPENS TO AN EXHAUST CHAMBER, THE IMPROVEMENT COMPRISING AN EXHAUST CHAMBER HAVING AN INLET ADAPTED TO RECEIVE GASEOUS FLUID FROM SAID POWER CHAMBER AND AN OUTLET CONSISTING OF NOZZLE MEANS, SAID EXHAUST CHAMBER HAVING A VOLUME AT LEAST 1.5 TIMES AS GREAT AS THE VOLUME OF SAID POWER CHAMBER AND HAVING A MINIMUM CROSS-SECTIONAL AREA OF FLOW BETWEEN SAID INLET AND SAID OUTLET AT LEAST 1.5 TIMES AS GREAT AS THE MINIMUM CROSS-SECTIONAL AREA OF FLOW OF SAID NOZZLE MEANS. 